On testing and/or lapping machines for gears, such as bevel or hypoid gears, the pinion and gear members are moved together to bring the pair into mesh, i.e. the pinion teeth engage the tooth slots of the ring gear/or vice versa. Once they are engaged, the pinion and gear can be moved together to the proper position and can then be rolled together in a desired testing or lapping procedure. Computer controlled multi-axis lapping and testing machines are well known and are readily available. Such machines are shown and described in, for example, U.S. Pat. No. 5,609,058 to Gnadt et al. and in Stadtfeld, Hermann J., "Single Flank Test, 3-D Vibration Analysis and Digital Imaging of Tooth Contact with PHOENIX.RTM. 500 HCT", The Gleason Works, Rochester, N.Y., June 1995.
In moving the gear members relative to one another to bring them into mesh, collisions between the toplands of the meshing may cause damage to machine components especially if a direct topland-to-topland collision occurs. If the collision is such that the toplands are offset from one another, chipping of the topland edges may occur especially if the gear is hardened. This situation can lead to chips staying between the teeth during subsequent rolling of the gear pair. In this instance, the chips are rolled into the surface of the teeth and scoring the gear set thus results. If the gears are not hardened and an offset topland-to-topland collision occurs, plastic deformation of the topland edges may result in which subsequent rolling may damage the gear set or at least it is necessary to remove the deformation (nick) by hand.
Methods have been proposed in an effort to properly bring mating gear members into mesh in machining or testing operations. Manual feeding of one member relative to another to bring mating members into mesh is well known. In this method, one member is incrementally fed toward the other member and as contact nears, rotational adjustments of one member are made such that the teeth of one member may engage the tooth slots of the mating member. While this method is reliable, it is extremely slow.
In the method disclosed in U.S. Pat. No. 2,150,313 to Bauer, a lever having an attached pin and dog is swung toward a pinion member and a ring gear-shaped shaving tool to which is mounted a backing plate having notches which are aligned with the tooth spaces of the shaving tool. The dog has a wedge-shaped nose portion and the notches have wide openings which converge rearwardly toward the back of the backing plate. The pin is inserted into a tooth space of the pinion which may require a manual rotational adjustment to align the pin with a pinion tooth slot. If the tool and pinion are positioned properly for meshing, the dog will simultaneously enter a notch of the backing plate. If the dog does not align directly with a notch in the backing plate, one of the sides of the nose portion of the dog will engage an inclined surface of a notch resulting in a small rotation of the tool as the dog becomes fully engaged with the notch. Once full engagement is achieved, the pinion and tool will be properly aligned. This method is also quite time consuming.
In U.S. Pat. No. 3,579,803 to Lautenschlager, a bevel gear pair to be lapped are brought into mesh by feeding one gear relatively toward the other. However, if contact of the tooth toplands occurs, the members of the gear pair are separated, the rotational position of one member is incrementally adjusted and the members of the gear pair are again brought into contact. The process is repeated if necessary. Also disclosed in this patent is a method of meshing wherein instead of separating members of a pair upon collision, one of the members is rotated to bring about proper alignment. While it is disclosed that a pressure relief valve is included to prevent build-up of heavy forces, either of these methods presents a risk of damage to the machine and/or gear members since a collision is permitted to occur before the inventive method is utilized.
Known from U.S. Pat. Nos. 3,717,958 to Ellwanger et al. and 3,795,143 to Deprez et al. are respective lapping and testing machines wherein during initial meshing, one member of the gear pair is rotated to facilitate the meshing process. However, this method is somewhat random as there is no control of the rotational positioning of either of the gear pair members to attain a proper meshing alignment. Thus, collisions may still be expected.
In some automatic CNC machines, another attempt to avoid damage due to collisions between tooth toplands during meshing is to include a spring-loaded device on a machine wherein movement of the spring is indicative of a topland collision. Although the gear members have collided, the machine components continue their programmed movement until movement of the spring alerts the machine controller to activate a particular slide to free the pinion and gear and rotate the ring gear a fraction of a pitch after which the machine will attempt to mesh the gear pair again. Although this procedure reduces many instances of damage, the procedure still permits forces to build in the machine due to a collision and as such, still presents the possibility of machine, or tooth, damage.
It is an object of the present invention to provide a method by which machine or tooth damage due to direct or offset topland collisions are reduced or eliminated by the avoidance of force build-up even in the event of such collisions.